1. Field of the Invention
The present invention relates to a digitizer tablet apparatus for input digital coordinate information to a computer system, such as CAD (Computer Aided Design) system, to digitally read graphic information. More particularly, this invention relates to a digitizer tablet apparatus suitable for reading maps or plat maps into a system which prepares drawings to be submitted when one files the registration of a real property, such as a land and a house. More specifically, this invention relates to an improvement of an input apparatus which is used to pick up positional coordinates in such a digitizer tablet apparatus.
2. Description of the Related Art
For example, a system which prepares drawings used in dealing in a real property, such as a land and a house, and for its registration often uses a digitizer tablet apparatus to read a map or an associated plat map as digital data.
In developing maps filed in the Ministry of Justice (e.g., plat maps, authenticated maps, etc. described in the Real Property Registration Act, article 17 in Japan) or drawings, which was drafted in dealing the same zone, on drawing data that are currently prepared by a drafting system, a digitizer tablet apparatus is often used to read data into the system.
Of course a digitizer tablet apparatus is widely used in reading drawings or the like other than those used in dealing in real properties or for their registration.
A digitizer tablet apparatus allows an operator to input positional coordinates in accordance with a drawing to be digitized (hereinafter referred to as "target drawing") on which original data is depicted, i.e., handwritten or printed data on a data sheet. There are several ways of inputting data, which include: inputting a train of continuous dots, inputting only predetermined coordinates and inputting coordinates every given time or every given distance. Popular input systems based on the input principle are an electromagnetic induction system, magnetostrictive system, resistive system and piezoelectric system. For example, the electromagnetic induction system electrically scans many coordinate lines, buried in a matrix form in a digitizer table of a digitizer tablet apparatus, and detects voltages induced on the coordinate lines in responsive to the magnetic flux generated by the exciting coil in the input apparatus that picks up coordinates from a data sheet. This system has a high resolution.
Input devices of any kinds, called free cursors or the like, which determine the input position in such a digitizer tablet apparatus, have substantially the same structure.
FIGS. 1 and 2 are a top view and a side view of an input apparatus used in a conventional digitizer tablet apparatus.
The input apparatus has a lens section 1 with a cross cursor for instructing the positional coordinates of a target drawing on a data sheet and an input operation section 2 which normally has a plurality of operation buttons 2A to input data. The lens section 1 is held on a part of the input operation section 2.
The conventional input apparatus shown in FIGS. 1 and 2 is often moved and operated while being nearly in contact to a data sheet on a digitizer table. To improve the operability, a bottom cloth 2B such as felt is adhered to the bottom of the input operation section 2. The lens section 1 with the cross cursor to instruct data points or the positions of measured portions of a zone is normally made of transparent plastics. To prevent the bottom of the lens section 1 from being stained or damaged by the friction in the sliding manipulation, therefore, its bottom is fixed, slightly lifted from the bottom of the input operation section 2.
As shown in FIG. 3, the bottom of the lens section 1 is lifted about 0.2 to 0.3 mm or more above a data sheet P as an input original. This distance or clearance causes a positional error between an intended input data point and actual input data, depending on the angle of view of the operator as shown in FIG. 4. This error is not negligible in drawings which demand high precision, such as drawings to be submitted in the registration of a real property.
Let us consider the case where data of a map with a scale ratio of 1:500 is read into a drafting system using a digitizer tablet apparatus. Suppose that an error of about 1 mm on the data sheet has occurred at the time data was input. This error is a deviation of about 500 mm or 50 cm in real scale. If a drawing to be submitted in the registration of a real property contains such a positional error, there is an inevitable error in the zone area, which significantly affect the interest of the applicant alone or the interests of the applicant and the neighbors. This type of a problem is likely to go into a lawsuit in an extreme case, and there are actually such lawsuits.
As described above, data error may occur due to the eye measurement, making the topography on a drawing to be submitted different from the actual topography. Such a difference in the area of a land is likely to cause a conflict between the persons concerned in this matter and to lead to a conflict over the money. In this respect, it is important to improve the input precision in the input apparatus.